The present invention relates to a method and device for monitoring the fuel/air ratio of the mixture of air and vapour being fed from the outlet of a fuel vapour accumulator.
It is known that recent antipollution regulations provide for automobiles to be provided with a vapour accumulator (canister) designed to absorb the fuel vapours which are formed, while the vehicle is parked, by the liquid fuel contained in the vehicle""s fuel tank. An accumulator of this type generally comprises a casing containing an activated carbon structure adapted to absorb the fuel vapour. An evaporative system is also provided which is adapted to carry out a vapour desorption stage (or scavenging) of the accumulator, in which the fuel stored in the activated carbon is desorbed and fed to the engine, in particular fed to the intake manifold of the engine. This evaporative system generally comprises a discharge duct which extends between an accumulator outlet and the intake manifold so as to utilise the vacuum created in the intake manifold when the engine is running and to provide a flow of air and vapour towards the intake manifold. The evaporative system further comprises an intake duct designed to allow the intake of air into the interior of said accumulator.
The evaporative systems of known type have a disadvantage in that the flow of air and vapour fed from the outlet is of variable and indeterminate composition; in particular, it is not possible to determine the percentage ratio of vapour fed to the manifold in relation to the total of vapour and air aspirated into the accumulator. Therefore, during the scavenging stage of the accumulator, a mixture of air and fuel is fed to the intake manifold, the percentage ratio of which mixture is not known. For this reason, during the aforementioned scavenging stage, the final air and fuel mixture which is fed to the engine may deviate from the stoichiometric ratio, which clearly brings about a deterioration in the emissions from the engine and in the operation of the catalytic converter.
The object of the present invention is to provide a device for monitoring the fuel/air ratio of the mixture of vapours being fed from the outlet of a fuel vapour accumulator.
This object is achieved by the present invention in that it relates to a device for monitoring the fuel/air ratio of the mixture of air and vapour being fed from the outlet of a fuel vapour accumulator of the type described in claim 1.
The present invention also relates to a method of monitoring the fuel/air ratio of the mixture of air and vapour being fed from the outlet of a fuel vapour accumulator of the type described in claim 6.